The discharge of granular materials from railroad cars has long presented a variety of problems. Traditionally a dedicated railroad siding was needed, often including a sunken pit beneath the railroad track in which was installed a gravity or mechanically operated conveyor. It was often inconvenient or even impossible to locate a plant near enough to such a siding to use the bulk unloading capabilities thereof.
More recently, pressure-type and vacuum-type pneumatic conveyors have been developed in which an adaptor is attached to the discharge gates of the railroad car. One or more pneumatic hoses are attached to the adaptor and the material is gravity-fed into the adaptor and conveyed away in the hoses via an airstream directed therethrough. While such pneumatic conveyors have represented a pronounced improvement over the fixed mechanical or gravity conveyors in sunken pits, a number of problems remain.
Such adaptors tend to be large and bulky, often requiring several workmen to lift and install them onto a railroad car. In addition, these adaptors must be tightly fitted to the car discharge gates and rigidly connected thereto. This is because, as the material is off loaded, the railroad car becomes lighter, thus rising under the influence of the spring suspension. The adaptor must rise with the car while maintaining the seal so that the material can be continuously unloaded without spillage.
There have been numerous prior attempts to produce an improved and more conveniently handled discharge adaptor.
In U.S. Pat. No. 2,813,640 to Loomis, a wheeled discharge adaptor is provided with a hydraulic jacking arrangement such that the adaptor can be wheeled beneath the railroad car and mechanically raised to meet the discharge gate. The hydraulic jacks are equipped with a manually operated jack handle disposed on the opposite side of the railroad car from the maneuvering handle for the adaptor itself. Material from the car discharge gates is gravity fed down an air charged inclined chute to a rotary airlock. The airlock is placed in a pneumatic pressure line for conveying the material from the airlock. The resulting adaptor, with the hydraulic jacks, rotary airlock and air-activated gravity flow chute, necessarily presents a relatively tall profile. Furthermore, in order to operate the jacks, a workman would first need to roll the adaptor under the railroad car and then cross to the other side of the car where he would manually raise the jacks to position the adaptor under the discharge gates. Should the position of the adaptor need to be adjusted during jacking, the workman would need to repeatedly cross from side to side of the car to first adjust the position and then commence jacking again.
In U.S. Pat. No. 5,125,771 to Herman et al., a wheeled adaptor is positionable under a railcar to be unloaded. As in the Loomis patent, a pair of manually operated jacks can then be manipulated to raise the adaptor into position in contact with the railcar discharge gate. The jacks in the Herman patent are mechanically operated screw jacks, including rotary handles which are positioned beneath the railroad car, thus requiring a workman to crawl beneath the car and physically crank the adaptor into position. In addition, the workman must alternate from side to side of the adaptor to incrementally raise the respective jacks to prevent the adaptor from tipping. The adaptor includes a rotary auger-type conveyor which carries material out an elongate tube to a pressure pneumatic or vacuum conveyor, where it is conveyed away. Again, as in the Loomis adaptor, the Herman adaptor requires a workman to wheel it into position and then raise it manually via a set of screw jacks to mate with a discharge gate. Unlike Loomis, with the screw jacks of Herman, no self-correcting leveling is accomplished as the railroad car rises. Thus, a workman needs to constantly adjust the screw jacks as the car rises, again necessitating crawling beneath the car and alternating from side to side of the adaptor.
The transportation and unloading of sugar, flour and other similar bulk dry granular or powder products present a unique set of problems. Traditionally sugar and flour have been hauled with "airslide cars" in which the sides of material storage hoppers slope to a discharge gate at approximately 10-15 degrees. Although these cars basically use a gravity discharge technique, with such a small slope of the hopper sides, air must be injected into the hopper from a separate fan via a manifold in the hopper itself to "fluidize" the material and allow it to flow to the discharge gate. Thus, an unloading station, in addition to the source of conveyor air for the pneumatic conveyor must have a separate fluidization blower, typically a 15 HP unit, to offload the sugar. Furthermore, the hauling capacity of such airslide cars is somewhat limited.
In response, Savannah Foods, a large sugar processing company, in conjunction with the Freight Car division of Trinity Industries, Inc., has developed a specialized center discharge railcar specifically designed for hauling sugar and similar bulk food products. This railcar has a capacity of approximately 260,000 lbs. of sugar, as opposed to approximately 190,000 lbs. for a typical airslide car. The improved center discharge car includes 3 separate hoppers, each of which slopes at approximately 40-45 degrees to a respective gravity-vacuum discharge gate. The increased carrying capacity and the increased hopper discharge slope of the railcar means that, when the railcar is fully loaded with sugar or the like, the clearance between the bottom of each discharge gate and the top surface of the railroad rails is approximately 14 inches. However, the requirement for a separate fluidization blower is eliminated. Each gravity-vacuum discharge gate is equipped with a slide gate and a movable vacuum chamber. With this arrangement, the cargo can be gravity discharged when both the slide gate and the vacuum chamber are opened, or vacuum unloaded via the vacuum chamber when just the slide gate is opened. However, many large volume sugar users, such as cereal and candy makers, have railcar sidings already equipped for unloading airslide railcars via positive pressure pneumatic conveyors and fluidization blowers and thus are not suitably equipped to unload a railcar with a gravity-vacuum discharge gate which requires the attachment of a vacuum pneumatic conveyor. Furthermore, since numerous airslide cars are still in use and will continue to be for some time to come, it is not economically viable to make any changes in unloading equipment which would prevent their use in unloading airslide railcars. Finally, due to the bare 14 inch clearance between the rails and the discharge gate, bulky, high-profile adaptors with air fluidized, shallow incline gravity feed chutes, such as that of Loomis, cannot be used with these railcars.
Accordingly, a need exists for an adaptor which would allow positive pressure pneumatic conveyors, such as those designed for use with airslide railcars, to be used to unload center discharge railcars equipped with gravity-vacuum discharge gates. Such an adaptor must be readily attachable and removable from both the railcar and the pneumatic conveyor, should be readily maneuverable by a single operator, and must present a profile height of less than 14 inches, i.e. the clearance between the rail top surface and the bottom of the gravity-vacuum discharge gate of a loaded railcar. Finally, such an adaptor, even with this low profile, must be equipped with an airlock to allow material to gravity flow from the railcar while preventing air pressure from the pneumatic conveyor from entering the railcar.